Such a control system is found, for example, on various types of working vehicles comprising a front and a rear part of a vehicle, which parts each have a frame and at least one wheel axle. The vehicle parts are connected to each other in such a way that they can pivot and the parts can be rotated in relation to each other around said pivot point by means of said two steering cylinders.
The invention will be described below in association with a working machine in the form of a wheel loader. This is a preferred, but in no way restricting application of the invention. The invention can also be used for other types of frame-steered vehicles, such as an articulated hauler.
The steering in a working machine must be very reliable. A loader usually has an ordinary steering wheel, but can, in parallel, also be equipped with steering by means of a lever. The steering wheel is used during transportation and the lever is used during work at lower speeds such as, for example, when loading trucks, as this is more comfortable for the driver.
A conventional control system comprises a pump that is driven by the vehicle's motor and that provides the steering cylinders with pressurized hydraulic fluid from a tank. A first hydraulic valve is connected mechanically to the steering wheel and is arranged on a conduit between the pump and the steering cylinders, whereby hydraulic energy is transferred to the steering cylinders when the driver turns the steering wheel. A second hydraulic valve, normally a proportional directional valve, is connected electrically to the steering lever via a control unit and is arranged on a conduit between the pump and the steering cylinders. Hydraulic energy is thereby transferred to the steering cylinders when the driver moves the lever.